The objectives of this study are to investigate the stimulatory actions of thyrotropin (TSH) and human thyroid stimulator (HTS) on thyroid cells in monolayer tissue culture. In preliminary studies a simple, efficient method has been developed for establishing dog and human thyroid cells in culture. The thyroid cell cAMP response to TSH stimulation is more sensitive than in any previously used thyroid preparation. This system, therefore, promises to be of great value in studies relating to the actions of TSH and HTS. It is planned to establish a sensitive bioassay for HTS activity in the serum of patients with Graves' disease, and to use this assay to correlate HTS activity with the clinical course and response to therapy in this disease. Using a mixed culture of human lymphocytes and human thyroid cells, it is hoped to develop an in vitro model for Graves' disease which may be used to further investigate the pathogenetic mechanism. Studies will be undertaken to investigate the mechanism of thyroid adenylate cyclase activation by TSH. The binding properties of (I-125)-TSH to cultured thyroid cells will be examined, in particular the relationship between the binding of near-physiological concentrations of TSH and cAMP generation. The effects of iodine, thyroid hormones and serum on this process will be studied. Finally, the role of cAMP and cGMP in thyroid hormone synthesis and secretion will be studied. Thyroglobulin secretion into the medium and latex-bead ingestion by the cells will be used as models for these respective functions.